The present exemplary embodiment relates to rotary sputtering targets and related assemblies. It finds particular application in conjunction with a rotary target assembly including a target material supported by a backing tube, and will be described with particular reference thereto. However, it is to be appreciated that the present exemplary embodiment is also amenable to other like applications.
Sputter depositions are reproducible and are also simple for process automation. High value materials such as gold, platinum and other alloys of precious metals, routinely find employment in thin film coatings using planar sputtering or evaporation deposition techniques. These techniques have limitations with respect to yield, speed of deposition and in cooperative in-line deposition of multi-layer stacks.
Rotary sputtering targets have been shown to improve the sputtering process. By rotating the sputtering material, the target material is sputtered in a more continuous uniform fashion than when compared to planar targets. Rotary sputtering targets are typically formed in a cylindrical shape. Using high value materials in cylindrical rotary systems as monolithic or heavy wall sleeves is typically prohibitively expensive. Accordingly, it is common to support a thinner sleeve of target material with a backing tube of a less expensive and/or stronger material. A backing tube provides added support while allowing more of the target material to be utilized before replacement.
A typical backing tube is constructed of a material that can withstand the sputtering process while retaining its shape. The backing tube supports the rotary sputtering target thereby reducing excess flexing of the target material. Another advantage of using a backing tube is that cooling fluid can be passed through the backing tube to cool the target material during the sputtering process. For cooling to be effective it is important that there is sufficient thermal contact between the cooling fluid and the rotary sputtering target material. Current technology for the assembly of rotary sputtering targets attach the backing tube in such a manner as to prevent any gap between the inner surface of the rotary sputtering target and the outer surface of the backing tube to ensure sufficient thermal contact between the backing tube and the target material.
There exist various techniques for attaching the rotary sputtering target to the backing tube. One such technique is to cast the rotary sputtering target onto the backing tube. This in essence creates a complete structure that is very rigid. However, casting is only feasible when using a castable rotary sputtering target material. Casting directly on the backing tube has its drawbacks. For example, casting often results in variable grain size and has an inherent porosity that is created from the volume changes of the liquid to solid transition. These variables and defects are detrimental to a target system.
Another technique for attaching the rotary sputtering target to the backing tube is by use of a bonding material. An adhesive or metal alloy is placed between the inner surface of the rotary sputtering target and the outer surface of the backing tube. This creates a strong bond between the two surfaces and assists in cooling transfer. However, care must be taken when flowing the adhesive between the rotary sputtering target and the backing tube to ensure adequate bonding strength. Reuse of the backing tube is a laborious process, as it is difficult to remove the remaining target material from a sufficiently secure bond. An improved bonding method and assembly is described in U.S. Patent Publication No. 2012/0006680, which is hereby incorporated by reference herein in its entirety.
While the method and assembly set forth in US 2012/0006680 offers an improvement over existing methods, there is still room for further improvement in both the method and the assembly.